Genetic and environmental effects on blood pressure in a Norwegian sample

Spousal similarities in cardiometabolic risk factors: A cross-sectional comparison between Dutch and Japanese data from two large biobank studies

BACKGROUND AND AIMS

Few studies have examined and compared spousal concordance in different populations. This study aimed to quantify and compare spousal similarities in cardiometabolic risk factors and diseases between Dutch and Japanese populations.

METHODS

This cross-sectional study included 28,265 Dutch Lifelines Cohort Study spouse pairs (2006-2013) and 5,391 Japanese Tohoku Medical Megabank Organization (ToMMo) Cohort Study pairs (2013-2016). Spousal similarities in cardiometabolic risk factors were evaluated using Pearson's correlation or logistic regression analyses adjusted for spousal age.

RESULTS

The husbands' and wives' average ages in the Lifelines and ToMMo cohorts were 50.0 and 47.7 years and 63.2 and 60.4 years, respectively. Significant spousal similarities occurred with all cardiometabolic risk factors and diseases of interest in both cohorts. The age-adjusted correlation coefficients ranged from 0.032 to 0.263, with the strongest correlations observed in anthropometric traits. Spousal odds ratios [95% confidence interval] for the Lifelines vs. ToMMo cohort ranged from 1.45 (1.36-1.55) vs. 1.20 (1.05-1.38) for hypertension to 6.86 (6.30-7.48) vs. 4.60 (3.52-6.02) for current smoking. An increasing trend in spousal concordance with age was observed for sufficient physical activity in both cohorts. For current smoking, those aged 20-39 years showed the strongest concordance between pairs in both cohorts. The Dutch pairs showed stronger similarities in anthropometric traits and lifestyle habits (smoking and drinking) than their Japanese counterparts.

CONCLUSIONS

Spouses showed similarities in several cardiometabolic risk factors among Dutch and Japanese populations, with regional and cultural influences on spousal similarities.

Genetic and environmental influences on blood pressure in an urban Indian population

Aggarwal Baniyas were found to have a high prevalence of high blood pressure. Genetic and environmental influences may be implicated for this risk factor of cardiovascular disease. The aim of this study was to investigate the potential for common genetic and environmental influences on blood pressure measures (systolic and diastolic blood pressure (SBP, DBP)). The population-based sample was comprised of 309 Aggarwal Baniya families, including 1214 individuals (271 fathers, 307 mothers, 311 sons and 325 daughters) from New Delhi, India. The prevalence of obesity in this community was found to be high (BMI: fathers, 26.1 kg/m2; mothers, 29.4 kg/m2; sons, 16.9-22.4 kg/m2; and daughters, 16.3-22.7 kg/m2). Correlation and heritability were estimated. Most sibling-sibling correlations were larger than the parent-offspring correlations, and all parent-offspring and sibling-sibling correlations were larger than the corresponding spouse correlation (SBP=0.026; DBP=0.029). The maximum heritability was estimated as 44.6% for SBP and 62.8% for DBP. The lack of a significant spouse correlation is consistent with little or no influence of the common familial environment. However, the high heritability estimate for both SBP and DBPs reinforces the importance of the non-shared environmental effect.

Heritability of blood pressure increases during mental stress

We studied the influence of mental stress on the contributions of genes and environment to individual variation in systolic (SBP) and diastolic (DBP) blood pressure by structural equation modelling in 320 adolescent male and female twins. Blood pressure data were collected during rest and during a reaction time and a mental arithmetic task. Univariate analyses of SBP and DBP showed familial aggregation for blood pressure. A genetic explanation for this resemblance was most likely, although during rest conditions a model that attributed familial resemblance to shared environmental factors, also fitted the data. There was no evidence for sex differences in heritabilities. Multivariate analyses showed significant heterogeneity between sexes for the intercorrelations of the blood pressure data measured under different rest and task conditions. Multivariate genetic analyses were therefore carried out separately in males and females. For SBP and DBP in females and for SBP in males an increase in heritabilities was seen for blood pressure measured during stress, as compared to rest measurements. The influence of shared environ-mental factors decreased during stress. For DBP in males no significant contributions of shared environment were found. The multivariate analyses indicated that the same genetic and environmental influences are expressed during rest and stress conditions.

Estimating the Extent of Parameter Bias in the Classical Twin Design: A Comparison of Parameter Estimates From Extended Twin-Family and Classical Twin Designs

Theclassical twin design(CTD) circumvents parameter indeterminacy by assuming (1) negligible higher-order epistasis; and (2) either nonadditive genetic or common environmental effects are nonexistent, creating two potential sources of bias (Eaves et al., 1978; Grayson, 1989). Because the extended twin-family design (ETFD) uses many more unique covariance observations to estimate parameters, common environmental and nonadditive genetic parameters can be simultaneously estimated. The ETFD thereby corrects for what is likely to be the largest of the two sources of bias in CTD parameter estimates (Keller & Coventry, 2005). In the current paper, we assess the extent of this and other potential sources of bias in the CTD by comparing all published ETFD parameter estimates to CTD parameter estimates derived from the same data. CTD estimates of the common environment were lower than ETFD estimates of the common environment for some phenotypes, but for other phenotypes (e.g., stature in females and certain social attitudes), what appeared as the common environment was resolved to be assortative mating in the ETFD. On average, CTD estimates of nonadditive genetic factors were 43% lower, and additive genetic factors 63% higher, than ETFD estimates. However, broad-sense heritability estimates from the CTD were only 18% higher than ETFD estimates, highlighting that the CTD is useful for estimating broad-sense but not narrow-sense heritability. These results suggest that CTD estimates can be misleading when interpreted literally, but useful, albeit coarse, when interpreted properly.

Spousal concordance for overall health risk status and preventive service compliance

PURPOSE

In this study we examined spousal concordance for two aggregate measures of health risk status and compliance with preventive service recommendations among 9620 pairs of cohabitating, opposite-sex married couples.

METHODS

Health risk appraisals were the primary data source to measure two outcome variables. Health risk status was compiled from 12 health risks and categorized into three levels (low-, medium-, and high-risk status). Overall preventive service compliance status was estimated by seven age-sex specific preventive service recommendations and dichotomized into lower and higher compliance status. For each of the husband and wife populations, we conducted proportional odds models and logistic regression models to assess spousal concordance for the two aggregate measures respectively. All models were adjusted for household income, one's characteristics (age, race, education, disease burden), and the same set of characteristics and the corresponding outcome variable from the spouse.

RESULTS

A positive correlation within spousal pairs was statistically significant for both health risk status and compliance status (p < .001) based on multivariate modeling. The odds ratios were similar in magnitude for the two spouse populations.

CONCLUSIONS

The analyses showed spousal concordance for aggregate measures of health behaviors. This study also provides some evidence for dominance of husband's education.

Genetic architecture of complex traits predisposing to nephropathy: hypertension

Blood pressure and hypertension have significant genetic underpinnings that may be age-dependent. The age-dependency, significant contributions from environmental factors such as diet and exercise, and inherent moment-to-moment variability complicate the identification of the genes contributing to the development of hypertension. Although genetic abnormalities may have moderate effects, the physiologic pathways involving these genes have redundant compensating mechanisms to bring the system back into equilibrium. This has the effect of reducing or completely masking the initial genetic defects, one of the hypothesized reasons for the small genetic effects found by the recent genome-wide association studies. This review article discusses the concept of initiators versus compensators in the context of finding genes related to hypertension development. A brief review is provided of some key genes found to be associated with hypertension, including the genes identified from the nine genome-wide association studies published to date.

Angiotensin-converting enzyme gene insertion/deletion polymorphism frequency in normotensive children with a positive family history of essential hypertension

AIM

To evaluate the possible relationship between blood pressure (BP) and angiotensin-converting enzyme (ACE) gene insertion/deletion (I/D) polymorphism in normotensive children with a positive family history of essential hypertension (EHT).

MATERIAL AND METHODS

Three hundred seventy-six randomly selected normotensive schoolchildren (147 boys, 229 girls) between the ages of seven and 17 years were enrolled. Children were subdivided into a 'first-degree relative group' and a 'second-degree relative group' according to the presence of EHT in parents or grandparents, respectively. BP was measured twice from the right arm and the systolic BP, diastolic BP and mean BP were recorded. ACE gene I/D polymorphism was performed from all studied children and frequency od DD, ID and ID allele were analysed in each study group.

RESULTS

Allelic frequencies of the DD genotype of the ACE gene were higher in children with a positive history in the first- (36.2%) and second-degree (38.3%) relatives for EHT than the controls (30.7%) (P < 0.05 for both). Children with a positive family history of EHT and a DD genotype, had significantly higher SBP, DBP and MBP levels (P < 0.05) than the children with ID or II genotypes.

CONCLUSION

We found that the ACE gene DD genotype was common and that BP levels were higher in Turkish children with a positive family history of EHT and DD genotype. Because the presence of DD allele might be the one of the potential contributor of EHT pathogenesis, further studies needed in large cohort for long term follow-up for EHT in children with DD allele.

Spousal concordance for major coronary risk factors: a systematic review and meta-analysis

Spousal pairs permit assessment of determinants of diseases related to environment, because they share the same lifestyle and environment. The authors reviewed spouses' concordance for the major coronary risk factors. A search of the MEDLINE, PubMed, and EMBASE databases was performed. Seventy-one papers were selected for a total of 207 cohorts of pairs and 424,613 correlations in more than 100,000 couples. The most strongly correlated within-pairs factors were smoking and body mass index, with overall correlations of 0.23 (95% confidence interval: 0.12, 0.36) and 0.15 (95% confidence interval: 0.05, 0.25), respectively. Statistically significant positive correlations were also found for diastolic blood pressure, triglycerides, total and low density lipoprotein cholesterol, weight, and the waist/hip ratio. The overall odds ratios for concordance in hypertension, smoking, diabetes, and obesity were all statistically significant, ranging from 1.16 to 3.25. Assortative mating influenced concordance for blood pressure, smoking, glucose, low density lipoprotein cholesterol, weight, body mass index, and waist circumference. This systematic review shows a statistically significant positive spousal concordance for the majority of main coronary risk factors. However, the strength of the concordance was markedly different among factors and appeared to be quite modest for all of them. Interventions to reduce cardiovascular risk factors should be addressed jointly to both members of a marital couple.

Repeated blood pressure measurements in a sample of Swedish twins: heritabilities and associations with polymorphisms in the renin-angiotensin-aldosterone system

BACKGROUND

Twin and family studies have shown that genetic effects explain a relatively high amount of the phenotypic variation in blood pressure. However, many studies have not been able to replicate findings of association between specific polymorphisms and diastolic and systolic blood pressure.

METHODS

In a structural equation-modelling framework the authors investigated longitudinal changes in repeated measures of blood pressures in a sample of 298 like-sexed twin pairs from the population-based Swedish Twin Registry. Also examined was the association between blood pressure and polymorphisms in the angiotensin-I converting enzyme and the angiotensin II receptor type 1 with the 'Fulker' test. Both linkage and association were tested simultaneously revealing whether the polymorphism is a Quantitative Trait Locus (QTL) or in linkage disequilibrium with the QTL.

RESULTS

Genetic influences explained up to 46% of the phenotypic variance in diastolic and 63% of the phenotypic variance in systolic blood pressure. Genetic influences were stable over time and contributed up to 78% of the phenotypic correlation in both diastolic and systolic blood pressure. Non-shared environmental effects were characterised by time specific influences and little transmission from one time point to the next. There was no significant linkage and association between the polymorphisms and blood pressure.

CONCLUSIONS

There is a considerable genetic stability in both diastolic and systolic blood pressure for a 6-year period of time in adult life. Non-shared environmental influences have a small long-term effect. Although associations with the polymorphisms could not be replicated, results should be interpreted with caution due to power considerations.

NHLBI family blood pressure program: methodology and recruitment in the HyperGEN network. Hypertension genetic epidemiology network

PURPOSE

Hypertension is a common precursor of serious disorders including stroke, myocardial infarction, congestive heart failure, and renal failure in whites and to a greater extent in African Americans. Large genetic-epidemiological studies of hypertension are needed to gain information that will improve future methods for diagnosis, treatment, and prevention of hypertension, a major contributor to cardiovascular morbidity and mortality.

METHODS

We report successful implementation of a new structure of research collaboration involving four NHLBI "Networks," coordinated under the Family Blood Pressure Program. The Hypertension Genetic Epidemiology Network (HyperGEN) involves scientists from six universities and the NHLBI who seek to identify and characterize genes promoting hypertension. Blood samples and clinical data were projected to be collected from a sample of 2244 hypertensive siblings diagnosed before age 60 from 960 sibships (half African-American) with two or more affected persons. Nonparametric sibship linkage analysis of over one million genotype determinations (20 candidate loci and 387 anonymous marker loci) was projected to have sufficient power for detecting genetic loci promoting hypertension. For loci showing evidence for linkage in this study and for loci reported linked or associated with hypertension by other groups, genotypes are compared in hypertensive cases versus population-based controls to identify or confirm genetic variants associated with hypertension. For some of these genetic variants associated with hypertension, detailed physiological and biochemical characterization of untreated adult offspring carriers versus non-carriers may help elucidate the pathophysiological mechanisms that promote hypertension.

RESULTS

The projected sample size of 2244 hypertensive participants was surpassed, as 2407 hypertensive individuals (1262 African-Americans and 1145 whites) from 917 sibships were examined. Detailed consent forms were designed to offer participants several options for DNA testing; 94% of participants gave permission for DNA testing now or in the future for any confidential medical research, with only 6% requesting restrictions for tests performed on their DNA. Since this is a family study, participants also are asked to list all first degree relatives (along with names, addresses, and phone numbers) and to indicate for each relative whether they were willing to allow study staff to make a contact. Seventy percent gave permission to contact some relatives; about 30% gave permission to contact all first degree relatives; and less than 1% asked that no relatives be contacted. Successes after the first four years of this study include: 1) productive collaboration of eight centers from six different locations; 2) early achievement of recruitment goals for study participants including African-Americans; 3) an encouraging rate of consent for DNA testing (including future testing) and relative contacting; 4) completed analyses of genetic linkage and association for several candidate gene markers and polymorphisms; 5) completed genotyping of random markers for over half of the full sample; and 6) early sharing of results among the four Family Blood Pressure Program networks for candidate and genome search analyses.

CONCLUSIONS

Experience after four years of this five-year program (1995-2000) suggests that the newly initiated NHLBI Network Program mechanism is fulfilling many of the expectations for which it was designed. It may serve as a paradigm for future genetic research that can benefit from large sample sizes, frequent sharing of ideas among laboratories, and prompt independent confirmation of early findings, which are required in the search for common genes with relatively small effects such as those that predispose to human hypertension.

Adult family members and their resemblance of coronary heart disease risk factors: the Cardiovascular Disease Study in Finnmark

Coronary heart disease tends to run in families, and the familial resemblance of major risk factors for the disease was examined among various types of adult family members. Family units were assembled from a total of 4,738 men and women who took part in a cross sectional health survey in four Norwegian municipalities where all inhabitants between 20 and 52 years of age were invited. After adjusting for age and other confounders, correlation coefficients were derived as a measure of the degree of resemblance. Viewed across all types of investigated familial relationships, similarity was found to be stronger for total cholesterol than for high-density lipoprotein cholesterol and triglycerides, and also stronger for systolic than for diastolic blood pressure. Between husbands and wives (3,060 subjects), correlations were small (between 0.02 and 0.06), except for 0.11 for total cholesterol. Lipid and blood pressure correlations ranged from 0.13 to 0.27 for parents and their offspring (471 subjects, p < 0.05) and from 0.11 to 0.22 among siblings (2,166 subjects, p < 0.01). Sibling correlations were consistent across age groups. Furthermore, reports from each individual on daily smoking (yes or no) revealed that husbands and wives had similar habits in 63.5% of all marriages as compared with the expected 49.4% had no smoking similarity at all been present. Smoking concordance was also demonstrated among siblings (p < 0.01). The persistent pattern of lipid and blood pressure aggregation among genetically related individuals from 20 to 52 years of age and the much weaker such similarity between husbands and wives, point towards genes or commonly shared environment at early ages as a major reason why coronary heart disease runs in families.

Genetics and behavioral medicine: risk factors for cardiovascular disease

This is the second in a series of three articles addressing the intersection of interests in behavioral genetics and behavioral medicine. In this article, we use risk factors for cardiovascular disease as a prototypical trait for which behavioral genetic approaches provide powerful tools for understanding how risk factors, behavior, and health outcomes are related. The approach synthesizes a number of methods and areas of interest in an attempt to arrive at a comprehensive, whole-organism understanding of health-related risk factors and their response to behavioral interventions.

Familial correlations, cohabitation effects, and heritability for cardiovascular risk factors

Familial correlations in cardiovascular risk factors were investigated with use of data from a community-based sample of 1319 nuclear families involving 4178 adult persons collected in the Busselton Population Health Surveys over the period 1966 to 1981. The risk factors considered were systolic blood pressure, diastolic blood pressure, body mass index, triceps fatfold, and cholesterol. All risk factors showed positive familial correlations, with correlations generally being lower for spouses than for parent-offspring pairs or for siblings. Spouse correlations showed little variation with age, suggesting that observed correlations are primarily due to assortative mating and not to cohabitation. The parent-offspring correlations tended to decline with age of (adult) offspring; this observation suggests that the effect of a shared household environment during childhood and adolescence diminishes over time when living apart during adulthood. The sibling correlations decreased with age for blood pressure and serum cholesterol and increased with age for body mass index and triceps fatfold. The estimated heritabilities were 27% for systolic and diastolic blood pressure, 37% for serum cholesterol, 52% for body mass index, and 23% for triceps fatfold. These results confirm that substantial familial aggregation of cardiovascular risk factors occurs and that much of this aggregation has a genetic basis, although assortative mating (in spouses) and environmental influences (in offspring and siblings) are also present. The nuclear family should be considered as a point of intervention in cardiovascular disease prevention programs.

Sibling correlations of coronary heart disease risk factors in a sample of Israeli offspring with parental history of myocardial infarction

Sibling correlations for coronary heart disease risk factors were analyzed in 731 pairs of siblings whose parents experienced a first myocardial infarction. Sibling correlations for lipids, lipoproteins and apolipoproteins ranged from 0.29 to 0.48, with limited changes on adjustment for sex, age, education and body mass index. For most lipid variables brother-brother correlation coefficients were highest and sister-brother correlation coefficients were lowest. Sib-sib correlation coefficients for lipids, lipoproteins, blood pressure and body mass index were similar to those estimated from a random sample of Jewish families. The sibling correlations were relatively low for waist to hip ratio, triceps and suprailiac skinfolds, moderate for subscapular skinfolds and body circumference measurements and high for number of cigarettes smoked by the siblings. The sibling correlations for lipid variables showed a moderate dependency on the apolipoprotein B XbaI genotypes. Siblings living in the same household tended to have higher correlation coefficients for HDL-C, apolipoprotein B and apolipoprotein AI than those living apart. The correlation coefficients for number of cigarettes and anthropometric variables tended to be heterogeneous due to the higher correlations among siblings living apart. A clear trend of decline in sib-sib correlations for apolipoprotein AI, glucose, cigarette smoking, body mass index and circumference measurements with increased spacing between sibling's ages was indicated. This temporal trend in sibling correlations for coronary heart disease risk factors suggests that genetic and/or environmental factors may have different influences at different ages.

Genetic and environmental influences on blood pressure in elderly twins

We used 289 pairs of Swedish twins reared apart or together to evaluate the importance of genetic and environmental influences on blood pressure. Unlike other twin and family studies, the adoption/twin design allows a distinction between estimates of the importance of shared rearing environments and genetic effects. Genetic factors were observed to play an important role for individual differences in blood pressure. Model-fitting analyses suggested upper limits of heritability for systolic and diastolic blood pressures in the entire sample of 0.44 and 0.34, respectively. More interestingly, substantial influences of shared family effects accounting for up to 27% of the variation were also revealed. Effects of correlated environment, which might reflect, for example, the intrauterine environment, existed to some extent later in life. The influence of genetic factors tended to decrease across age groups for systolic blood pressure (0.62 in individuals less than 65 years old; 0.12 in those 65 years and older) but not for diastolic blood pressure (0.22 for the middle-aged group; 0.26 for the older group). However, this declining trend for systolic blood pressure did not reach significance (chi 2 = 8.07, df = 4, P = .09).

Age-specific genetic effects for blood pressure

Correlations between relatives were determined for systolic and diastolic blood pressure. The correlations decrease as age differences between relatives increase in a Norwegian sample with 43,751 parent-offspring pairs, 19,140 pairs of siblings, and 169 pairs of twins. A simple biometric model specifying only age-specific genetic additive effects and environmental effects fitted well to correlations between cotwins, pairs of siblings, and parent-offspring dyads in subsets of relatives grouped by age differences. None of the environmental effects appeared to be due to environmental factors that are shared by family members. Models that excluded a parameter for the age-specific genetic influence did not fit the data. The results may partly explain what seems to be a discrepancy between relatively low parent-offspring correlations from previous nuclear family studies and high correlations from twin studies, especially in identical twins.